LIGHT DETECTION CIRCUIT FOR AMBIENT LIGHT AND PROXIMITY SENSOR
A circuit for implementing an ambient light sensing mode and a proximity sensing mode includes a light sensor, a light source, and a controller coupled to the light sensor and the light source. The controller is configured to process outputs from the light sensor before and after the light source is energized to obtain an ambient light level output and to compare the ambient light level output with an output from the light sensor when the light source is energized to implement the proximity sensing mode.
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This application is a continuation of U.S. application Ser. No. 12/589,360, filed Oct. 22, 2009, which claims the benefit of U.S. Provisional Patent Application No. 61/107,594 filed Oct. 22, 2008, each of which is incorporated by reference herein in its entirety.
REFERENCE REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable
SEQUENTIAL LISTINGNot applicable
BACKGROUND OF THE INVENTION1. Field of the Disclosure
The present disclosure relates to ambient light and proximity sensors.
2. Background of the Disclosure
Sensors, such as ambient light sensors or proximity sensors, have been developed and incorporated into electronic devices, such as smart phones, personal digital assistants, personal computers or laptops with touch screens, kiosks, and various other types of electronic appliances, games, toys, etc. Such electronic devices commonly include displays that are illuminated to facilitate interaction with a user and ambient light and/or proximity sensors can be used to control the illumination of such displays. In one example, an ambient light sensor is used to adjust the illumination of the display in varying ambient light levels. In another example, a proximity sensor is used to illuminate the display only when a user is detected in a certain proximity to the device in order to conserve power.
SUMMARY OF THE INVENTIONIn one example, a circuit for implementing an ambient light sensing mode and a proximity sensing mode includes a first light sensor that is more sensitive to light in the infrared spectrum than to light in the visible spectrum and a light source that emits light in the infrared spectrum. The circuit further includes a second light sensor that is sensitive to light in the visible spectrum and a controller coupled to the first light sensor, the light source, and the second light sensor. The controller is configured to process an ambient light level output from the first light sensor without the light source energized with an output from the first light sensor with the light source energized to implement a proximity sensing mode. Further, the controller is configured to process an output from the second light sensor to implement an ambient light sensing mode.
In another example, a light sensor circuit includes a light sensor and one or more calibration sensors disposed around the light sensor. The light sensor is coupled to an output pin and a bias voltage is applied to the one or more calibration sensors to enhance the sensitivity of the light sensor.
In a further example, a circuit that models a typical human visual system response to visible light intensity includes a first light sensor that is sensitive to both visible light and infrared light and a second light sensor that is more sensitive to light in the infrared spectrum than to light in the visible spectrum. A controller is coupled to the first and second light sensors to process the outputs from the first and second light sensors to model the typical human visual system response to visible light intensity.
In one example, the present disclosure provides a light sensor design that is more sensitive to light in the infrared (“IR”) spectrum than to light in the visible spectrum.
In another example, a light sensor that is sensitive to visible and IR light (“Visible+IR sensor”) and a light sensor that is more sensitive to IR light (“IR sensor”) are used together to result in a light sensor to model a typical human visual system response to visible light intensity. The method to derive the model of the human visual system response can utilize a mathematical function represented by the formula: Z=aX+bY+c, where X is an output from the Visible+IR sensor, Y is an output from the IR sensor, Z is a resulting parameter that models the light intensity seen by a typical human visual system, and the parameters a, b, and c are constants that can be derived from empirical testing. In various other embodiments, the parameters a, b, and c can be temperature dependent and/or the equation can generally be in the form of Z=f(X, Y), wherein Z is any combination of mathematical functions of X and Y, e.g., Z=aX+bY+cX2+dY2+eXY+f.
In yet another example, a single light sensor is designed to model the typical human visual system response to visible light intensity.
Further, the light sensors disclosed herein can be configured as dark current reference sources. The output from such dark current reference sources can be used to offset the effect of dark current in any of the light sensors disclosed herein.
Another aspect of the present disclosure includes a detector chip design that incorporates one or more light sensors. In one embodiment, the detector chip includes a pixel matrix of one or more calibration sensors that surround a light sensor. An output line is coupled to the light sensor, a bias voltage is coupled to the calibration sensor(s), and the light sensor and calibration sensor(s) are further coupled to the same ground to provide more accurate light measurements. Further, the detector chip can include a guard ring that surrounds the pixel matrix to reduce further the sensitivity of the chip to noise. In one example, the guard ring is made of a P+ layer.
The present disclosure also provides a circuit that incorporates one or more of the light sensors disclosed herein to give an accurate light reading with low noise. Various processes or algorithms are also disclosed that can be implemented to allow a single chip to provide both ambient light sensing and proximity sensing functions, to minimize or compensate for ambient light noise conditions, and to minimize power consumption during ambient light sensing and proximity sensing functions.
In one example, a light sensor that is sensitive to visible and IR light (“Visible+IR sensor”), e.g., the photodiode 10 of
In another example, the use of the mathematical function described above to provide a light sensor that models the typical human visual system response to visible light intensity is made unnecessary through a photodiode 50 illustrated by
In
Referring now to
Referring more specifically to
Referring to
Various modifications can be made to the processes of
Referring to
Referring to
In yet another operating mode, a light sensing chip is put into an “idle” mode during which most of the chip functions are turned off to save power. During the idle mode, only a low power clock is active to keep track of the idle time. The chip is activated periodically to perform the ambient light sensing or proximity sensing functions. The ratio of measurement (active) time vs. idle time can be from about 1:1 to 1:99.
Other embodiments of the disclosure including all the possible different and various combinations of the individual features of each of the foregoing described embodiments are specifically included herein.
INDUSTRIAL APPLICABILITYThe present disclosure provides various sensor designs, circuits incorporating such sensor designs, and processes to control such circuits to determine ambient light levels and to function as proximity sensors.
Numerous modifications to the present disclosure will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the disclosure and to teach the best mode of carrying out the same. The exclusive right to all modifications within the scope of this disclosure is reserved.
Claims
1. A circuit for implementing an ambient light sensing mode and a proximity sensing mode, comprising:
- a light sensor;
- a light source; and
- a controller coupled to the light sensor and the light source, wherein the controller is configured to process outputs from the light sensor before and after the light source is energized to obtain an ambient light level output and to compare the ambient light level output with an output from the light sensor when the light source is energized to implement the proximity sensing mode.
2. The circuit of claim 1, wherein the controller is configured to compare the ambient light level output with the output from the light sensor with the light source energized to implement the proximity sensing mode only if the ambient light level output is higher than an ambient light threshold value.
3. The circuit of claim 1, wherein the controller is configured to calculate a difference between the output from the light sensor with the light source energized and the ambient light level output to implement the proximity sensing mode.
4. The circuit of claim 3, wherein the controller is configured to compare the difference to a proximity threshold value to determine if the light sensor has detected an object in proximity thereto.
5. The circuit of claim 1, wherein the light sensor is more sensitive to light in the infrared spectrum than to light in the visible spectrum.
6. The circuit of claim 5, wherein the light sensor includes a P-type substrate with an N-type well formed over the P-type substrate, an N+ doped region disposed within the N-type well, P+ doped regions disposed on opposing sides of the N-type well, and a filter layer disposed over the P-type substrate for shifting the spectral response of the first light sensor toward the infrared spectrum,
7. The circuit of claim 6, wherein the filter layer is a poly silicon layer.
8. The circuit of claim 6, wherein the light sensor further includes a dielectric layer disposed over the P-type substrate and the filter layer is disposed in the dielectric layer.
9. The circuit of claim 8, wherein the filter layer is a poly silicon layer.
10. The circuit of claim 1, wherein the light source emits light in the infrared spectrum.
11. The circuit of claim 1, further comprising one or more calibration sensors disposed adjacent the light sensor, wherein the light sensor is coupled to an output pin and a bias voltage is applied to the one or more calibration sensors to enhance the sensitivity of the light sensor.
12. The circuit of claim 11, further comprising a guard ring disposed round the light sensor and the one or more calibration sensors.
13. The circuit of claim 12, wherein the guard ring primarily comprises a P+ doped layer.
14. The circuit of claim 11, further comprising a plurality of calibration sensors that surround the light sensor.
15. The circuit of claim 11, wherein the one or more calibration sensors provide one or more dark current reference values to the controller.
16. A light sensor that is more sensitive to light in the infrared spectrum than to light in the visible spectrum, comprising:
- a P-type substrate;
- an N-type well formed over the P-type substrate;
- an N+ doped region disposed within the N-type well;
- P+ doped regions disposed on opposing sides of the N-type well; and
- a filter layer disposed over the P-type substrate for shifting the spectral response of the first light sensor toward the infrared spectrum.
17. The light sensor of claim 16, wherein the filter layer is a poly silicon layer.
18. The light sensor of claim 16, further comprising a dielectric layer disposed over the P-type substrate, and wherein the filter layer is disposed in the dielectric layer.
19. The light sensor of claim 18, wherein the filter layer is a poly silicon layer.
20. A light sensor that models a typical human visual system response to visible light intensity, comprising:
- a P-type substrate;
- an N-type well formed over the P-type substrate;
- an N+ doped region and a P+ doped region disposed within the N-type well;
- a P-type terminal disposed on a side of the N-type well; and
- a dielectric layer disposed over the P-type substrate.
Type: Application
Filed: May 27, 2011
Publication Date: Nov 3, 2011
Patent Grant number: 8097851
Applicant: EMINENT ELECTRONIC TECHNOLOGY CORP. (Hsinchu)
Inventors: Tom Chang (Los Alto, CA), Andrew Grzegorek (San Jose, CA), Chongmei Zhang (Cupertino, CA), John Canfield (Union City, CA)
Application Number: 13/117,978
International Classification: G01J 5/20 (20060101); H01L 31/0232 (20060101); H01L 31/0216 (20060101); H01J 40/14 (20060101);